1. Field of the Invention
The present invention relates to a numerical controller, and particularly to a numerical controller that automatically performs acceleration/deceleration control in table-format-data-based operation.
2. Description of the Related Art
As a method for driving and controlling controlled axes in synchronization with one another in synchronization with motion of a reference axis, there is a known table-format-data-based operation function of storing information on the positions of the controlled axes in table format data provided in a memory or any other component in correspondence with the position of the reference axis and operating the controlled axes in synchronization with the reference axis on the basis of the information stored in the table format data.
Japanese Patent Laid-Open No. 2003-303005 discloses a numerical controller that performs numerical control called a path table operation function or electronic cam control using the table-format-data-based operation function. The numerical controller allows arbitrary tool action free from a machining program, whereby the machining period can be shortened and high-precision machining can be achieved.
In the table-format-data-based operation disclosed in Japanese Patent Laid-Open No. 2003-303005, when table-format-data-based operation shown in FIG. 8 is performed, a controlled axis linearly moves between command blocks (moves at constant speed) and is therefore abruptly accelerated and decelerated, resulting in large impact acting on a machine being controlled.
To reduce the impact associated with the abrupt acceleration and deceleration, an operator needs to add command blocks for acceleration and deceleration to the table format data.
Japanese Patent Laid-Open No. 2007-304714 discloses a technology for performing acceleration/deceleration control by using quadratic/cubic function connection in table-format-data-based operation. When the technology is used, a controlled axis moves between two points with constant acceleration applied in the quadratic function connection, or moves with constant jerk applied in the cubic function connection.
FIG. 8 shows an example of typical table format data. In the table format data illustrated in FIG. 8, a set of a reference value expressed in the form of a command L and an X coordinate or a Y coordinate expressed in the form of a command X, Y, or any other coordinate is written in one line, and a plurality of lines are specified. The thus configured table format data commands the numerical controller to move an axis to a specified coordinate value at a specified reference value.
When acceleration and deceleration are applied in the typical table-format-data-based operation shown in FIG. 8, gentle acceleration and deceleration are performed at the start point and the end point of driven axis action that are specified by the table format data, but the controlled axis does not reach the specified coordinate value at the specified reference value (reference time), undesirably resulting in a discrepancy between the action specified by the table format data and the actual action of the controlled axis.
FIG. 9 shows motion of a controlled axis in the form of graphs in a case where an acceleration/deceleration technology is applied to the operation based on the table format data <TIME_TABLE_0101_X> shown in FIG. 8. As shown in FIG. 9, when acceleration/deceleration control is performed at the start point and the end point by using an acceleration/deceleration period t, the controlled axis does not reach X200.0, which is the end point, at a reference value L2000.0. If the action of the controlled axis shown in the upper graph of FIG. 9 is inverse-transformed to table format data, it is found that the content of the inverse-transformed table format data differs from the content of the original table format data <TIME_TABLE_0101_X>, as indicated by the table format data <TIME_TABLE_0201_X> shown in the lower section of FIG. 9.
As described above, when acceleration/deceleration is applied to typical table-format-data-based operation, the relative relationship between a specified reference value and the coordinates of the controlled axis deteriorates, and the controlled axis undesirably cannot be synchronized with the other axes. Therefore, to add command blocks for acceleration/deceleration to the table format data, the operator needs to calculate necessary acceleration/deceleration and write acceleration and deceleration command blocks that explicitly reflect a result of the calculation in the table format data. FIG. 10 shows an example of table format data to which the operator adds acceleration and deceleration command blocks in consideration of the relative relationship between a reference value and the coordinates of the controlled axis. As shown in FIG. 10, the operator needs to calculate in advance a time constant t and a travel α associated with the acceleration/deceleration and create by himself/herself table format data <TIME_TABLE_0301_X> in which a result of the calculation is incorporated.
It is therefore difficult for the operator to create table format data, and the operator further needs to write acceleration and deceleration command blocks, undesirably resulting in an increase in the size of the table format data and an increase in the program volume.
The same holds true for a case where the technology disclosed in Japanese Patent Laid-Open No. 2007-304714 is used. FIG. 11 shows an example in which the technology disclosed in Japanese Patent Laid-Open No. 2007-304714 is used to add commands to perform acceleration/deceleration to table format data. When the quadratic/cubic function connection disclosed in Japanese Patent Laid-Open No. 2007-304714 is introduced, integrating the acceleration segment program and the deceleration segment program with each other into a single block reduces the size of the table format data to a small value, but the operator still undesirably needs to create table format data including pre-calculated time constant t and travel α associated with the acceleration/deceleration.